This invention relates to detectors for detecting Radio Frequency (RF) imbalances between radio frequency amplifiers.
Dual radio frequency (RF) amplifiers are used to increase the output power of radio frequency amplifiers beyond the power capabilities of the amplifying components and require, for maximum efficiency, that each amplifier provide equal amplification to the signal that is being amplified. In the event that one of the RF amplifiers outputs is degraded, corrective action must be taken to prevent damage if the dual radio frequency amplifiers are to continue operation. If corrective action is not taken, one amplifier, in order to compensate for the degraded output of the other amplifier, will be, in the prior art circuits, overdriven in order to maintain the desired output power of the dual radio frequency amplifiers. This can lead to signal degradation as well as failures of the amplifying components. Thus, the output from both RF amplifiers must be monitored.
In the prior art the amplifiers were monitored either by thermal sensing, DC power supply current sensing or sensing DC analogs of the RF voltage. Each of the above methods of monitoring the RF amplifiers has several drawbacks. For example, thermal sensing has been found to be very slow acting, and is difficult to install because of the requirement of simultaneously providing a thermal bond and electrical isolation. DC current sensing of the DC power supplies will indicate a catastrophic failure but this method is generally unreliable for detecting degradation in the performance of the amplifiers. Obtaining a DC voltage analog or rectified representation of each RF output signal is an improvement over the other two methods, however, no phase information is provided and harmonic distortion is a problem. Although fault indication may be either a positive or negative DC voltage, it is normally a low DC voltage output and is thus difficult to monitor.